Stable pulse generator



Sept. 24, 1946. w D. o. GRIEG STABLE PULSE GENERATOR Filed Dec. 20, 194117/6 VOLMGE' DOA/ALP a 6/?76'6' Patented Sept. 24, 1946 2,408,061 STABLEPULSE GENERATOR Donald D. Grieg,

New York, N. Y., assignor to Federal Telephone and Radio corporation ofDelaware Corporation, a

Application December 20, 1941, Serial No. 423,862

2 Claims. (Cl. 250'36) This invention relates to improved means for thegeneration of short impulses of relatively high energy and periodicallyrecurrent.

It is an object of the invention to provide relatively simple means forthe generation of impulse energy.

Another object is to provide an improved stabilized impulse generatorwherein it is not necessary to synchronize the generator to an externalfrequency standard.

A further ebject is to provide an improved impulse generator wherein theimpulse frequency is independent of load or supply-voltage variations.

It is also an object to provide an improved impulse generator whereinthe impulse width is constant over a range of supply voltage or loadconditions.

A still further object is to provide an improved impulse generatorwherein the impulse recurrence frequency may be varied and the width ofimpulses at the same time maintained constant in spite of such frequencyvariation.

Other objects and further features of novelty and invention willhereinafter be pointed out or will become apparent from a reading of thefollowing specification in conjunction with the drawing includedherewith. In said drawing, Fig. 1 is a schematic diagram of a circuitincorporating features of the invention, and Fig. 2 illustratesgraphically the progressive treatment of wave forms in the circuit ofFig. 1.

Broadly speaking, the invention contemplates the generation of impulseenergy by applying regularly recurrent current surges across aninductance whereby correspondingly recurrent damped oscillations are setup in the circuit of the inductance. Appropriate shaping meansthereafter serve to remove all of such oscillations but the firstcurrent surge thereof.

Specifically, and in accordance with the preferred form shown in Fig. 1,an oscillator feeds an electron-coupled device to supply the regularlyrecurrent current surges. In the form shown, the circuit of thisoscillator includes a vacuum tube T1 of known form having a cathode,control grid, screen grid, suppressor grid, and anode. The oscillatorycircuit further comprises the parallel impedance combination of aninductance L1, a variable capacitance C1, and another capacitance C2.The frequency of oscillation of this circuit is largely determined bythe magnitudes of elements L1, C1 and C2, and this frequency may bedefined as In operation the oscillator functions with the screen grid,control grid, and. cathode circuits 2 of tube T1 to produce asinusoidally varying voltage of the form shown in Fig. 2a.

The remaining elements of tube T1 preferably form an amplifier foramplifying portions of the voltage generated by the abovedescribedoscillator. Preferably, in accordance with the invention, the suppressorgrid of tube T1, which forms an effective control grid for theamplifier, is biassed below cutoff so that class C operation of theamplifier results. It will be clear that the output of tube T1 will thencomprise a series of current surges or pulses, the duration of which isdetermined by the degree to which the amplifier portion of tube T1 isoperated class C, that is, the magnitude of negative bias applied to thesuppressor grid across the used portion of resistance Rs. Preferably,this bias is relatively great so that only very short current surges arederived in the output of tube T1. These current surges may be of theform shown in Fig. 2b.

In accordance with features of the invention,

the output of tube T1 is applied directly across an inductance L2. Now,when the above-mentioned short pulses of current fiow through inductanceL2, voltage surges of high value may appear thereacross, as will beclear. Inasmuch as there is unavoidably some capacity associated withinductance L2 and its associated circuit, the nature of the voltagepulses appearing across L2 will be damped oscillations, as shown forexample, in Fig. 2c.

Now, in order to obtain relatively high voltage pulses of short durationfrom these damped oscillations, I propose to use appropriate shapingmeans for eliminating all of the voltage variations but the initialsurge associated with these pulses. Several methods for so shaping theoutput appearing across inductance L2 will naturally occur to thoseskilled in the art. For example, it would be possible to shuntinductance L2 with resistance, thereby increasing the damping andfurther reducing any effect of the undesired voltage variations. Theobjection to this method is that the. initial pulse is likewiseconsiderably reduced in amplitude, and at the same time its width at thebase is substantially broadened due to the effect of such a shuntresistor on the time constant of the damped oscillation circuit.

In accordance with thejinvention, however, I propose to employthermionic damping means shunted across inductance L2 in order to removethe undesired voltage variations following the initial pulse. In theform shown, a diode T2 is connected across inductance L2, and a resistorR3 is preferably in series therewith to reduce the effect of theplate-cathode capacitance of the diode. The operation of such aconnection will be readily apparent. Assuming the initial pulse acrossinductance Le to be positive, the cathode may be controllable in anydicated by the arrow traversing this element.

3 of diode T2 will be positive with respect to the plate thereof. Nocurrent will then flow through the diode, and the diode shunting efiectwill be negligible. During the negative cycle of oscillation immediatelyfollowing the initial pulse, diode T2 will be conductive, thuseffectively shunting inductance L2. The removal of a voltage surgeacross inductance L2 in this manner immediately removes any cause for,further and lesser voltage variations, It follows, therefore, that onlysingle pulses corresponding to the initial surge of voltage acrossinductance L2 will appear across inductance L2 when diode T2 isconnectedas shown. It is to be noted that in the preferred form ofeliminating the undesired voltage surges, the amplitude of the initialsurge is not noticeably affected, and successive lesser surges arecompletely eliminated.

Inasmuch as the width of pulse generated in the above manner dependsupon the damped oscillation frequency, any desired control over suchwidth (within limits, of course) may be effected by varying a circuitconstant within the damped oscillation circuit. For example, inductanceL2 known manner as in- Appropriate output may be derived from theabove-described circuit by well known means. In

the form shown, a socalled cathode follower amplifier circuit isemployed. This amplifier circuit includes a vacuum tube device T3, andthe output pulses may be obtained therefrom in a load P1 across a lowmagnitude resistor R4 in the cathode, circuit of tube T3. In the formshown, a coupling condenser C3 in the input circuit of tube T3 ispreferably made small in order to reduce the shunting effect of theinput to tube T3, and a grid resistor R2 is also small in order not toincrease the width of pulses due to the abovenoted undesirable dampingeffect of excessive resistance.

It will be noted in connection with the pulse generator described thatsince the pulse frequency isdetermined solely by the sinusoidaloscillator frequency, the frequency of pulse output may be varied byappropriate control of the oscillator, as by varying condenser C1, forexample. The amplifier and oscillator sections of tube T1 are isolatedfrom each other with the exception of a coupling by the electron streamin this tube. It follows that the pulse generator will have thedesirable feature that variation in load output may not affect the pulsefrequency. Furthermore, in accordance with well known methods, theoscillator may be made to supply a frequency substantially independentof supply voltage by proper adjustment of the cathode tap on inductacneL1 and adjustment of the screen grid voltage by posignal.

modifications may be made fully within the scope thereof. For example,if it is not desired to have a flexible variation of impulsefrequencies, a crystal oscillator may be employedinstead of theoscillator described. Such an oscillator would, of course, furnish apermanently reliable and stable pulse frequency,

Furthermore, time modulation of the pulses generated bythe circuitdescribed may be obtainedby the relatively simple expedient of varyingsome circuit constant in the damped oscillation circuit in accordancewith an intelligence ,Such modulation may be effected in a relativelysimple manner, say by varying the inductance of L2 in accordance withthe intelligence signaL as will :be clear.

What I claim is: V 1. Pulse'generator comprising, in combination, avacuum tube having control elements including an anode, a cathode and agrid, and a high internal plate resistance characteristic, a tankcircuit, means interconnecting said tank circuit with elements of saidvacuum tube to produce oscillations therein, an output circuit connectedbetween the anode and cathode of said tube, means biasing an element ofsaid vacuum tube to sucha value as to produce periodically recurrentcurrentsurges in said output circuit, a tun able inductive reactorserially connected in said output circuit, said reactor having aresistance value relatively small compared with the internal resistanceof said tube, a um-directional rectifier connected in shunt with saidinductive reactor,

tentiometer R1. For any fixed value of control A means deriving inducedvoltage pulses from said reactor when said current surges from saidvacuum tube are impressed thereon, and means to produce the maximumvoltage pulses possible from the time duration of the applied currentsurges, comprising means varying the bias of the vacuum tube element andmeans varying the tuning of saidreactor.

2. The combination according to claim 1, in whichsaid vacuum tubeincludes a suppressor grid, and said biasing means includes means for onsaid suppressor grid.

varying the bias DONALD D. GRIEG.

shown, it is to be understood that many

